(1) Field of the Invention
The present invention relates to a direct-feed type writing implement.
(2) Description of the Prior Art
Conventional direct-feed type writing implements which use so-called raw ink, i.e., liquid ink, are known to employ an ink collector making use of capillary action, e.g., of a vane-like regulator or a fiber bundle for temporal retention of ink, in order to prevent ink leakage due to expansion of the air inside the ink tank accompanying change in ambient conditions such as reduction in pressure and/or increase in temperature.
In a writing implement using the ink collector, in order to positively prevent forward leakage of ink from the writing point side, the size of the ink collector is designed based on the maximum expansion, estimated from the ink tank volume. Therefore, the design of the size of the ink collector depends on the size of the ink tank. That is, the larger the ink tank, the greater the ink collector needs to be.
However, forming a larger ink collector means more cost. There is another drawback in that making the ink collector larger in diameter results in the loss of stylish appearance. Alternatively, if the ink collector is long, the feeder means such as a center core or the like which penetrates through the ink collector and leads ink to the writing portion becomes long, so that the long collector configuration produces disadvantages as to forward leakage since the head of ink acts on the writing portion.
In general, it is well known that the ink retention volume of the ink collector is set at 10 to 30% of the ink tank volume. However, there have been demands for the reduction of the size of the ink collector while keeping the ink tank size, or for enlarging the size of the ink tank while keeping the ink collector as is.
Conventionally, a configuration using an ink absorber provided in the ink tank is disclosed in Japanese Patent Application Laid-Open Hei 4 No. 227886. As shown in FIGS.1 to 3, this configuration includes a capillary liquid retainer 215, i.e., the ink absorber as a center core for feeding ink to the writing tip 212 and an air supply pipe 213. This conventional configuration is an applicator 210 wherein a liquid suctioning device 216 is isolated at a position when the writing point is set approximately downwards. Actually, when the writing point is oriented downwards as in normal writing, no ink is supplied to liquid suctioning device 216, hence the ink reserved in liquid suctioning device 216 is the only ink supply for writing, resulting in a short writing distance.
A further description about the prior art disclosed in Japanese Patent Application Laid-Open Hei 4 No. 227886 will be made with reference to FIGS. 1 to 3. In applicator 210, air supply pipe 213 allows a liquid container 211 to be filled with air equal in volume to that of outflow of liquid 217 and also is to prevent liquid 217 from flowing through the opening formed in air supply pipe 213 and directing the liquid into air 214, in cooperation with a space 227 or a capillary medium 226 provided in the space 227. This means that no ink will enter air supply pipe 213 and will be supplied to the writing portion and ink supply to the writing portion is provided only by liquid 217 stored in capillary liquid retainer 215. Therefore, in this conventional case, the ink reserved in the capillary liquid retainer is the only ink supply, resulting in a short writing distance, as described above.
Japanese Patent Application Laid-Open Hei 4 No. 227886 also discloses a prior art configuration shown in FIG. 2 in which liquid 217 is stored in a contractile tube 224 accommodated in an inner space 225 of liquid container 211 so as to fill almost the entire inner space 225 with liquid 217. This means that if no contractile tube is used, the entire inner space 225 cannot be filled up with liquid 217, i.e., ink. The fact that liquid 217 cannot fill the entire inner space but can only fill up to about half, is obvious in FIG. 1 and in another embodiment shown in FIG. 3. Therefore, in order to fill the whole container of the ink tank with ink, the above-mentioned tube is a must. Therefore, configurations without such a tube have the drawback in that inner space 225 or the entire ink tank cannot be filled up with ink.
On the other hand, in the case where inner space 225 or the ink tank using such a tube is filled with ink, the following problem occurs. When the tube is formed of rubber or the like having elasticity, the pressure due to contraction of the rubber or the like is continuously applied to liquid 217 or the ink. This situation is the same when the writing point is set upwards. In the conventional configuration shown in FIG. 2, disclosed in Japanese Patent Application Laid-Open Hei 4 No. 227886, since liquid 217 is able to enter capillary liquid retainer 215 due to the function of a valve means 220 when the writing point is set upwards, the ink under pressure infiltrates capillary liquid retainer 215, causing leakage from the tip, designated at 212. When the tube is formed of a non-elastic material, no pressure from elasticity acts on the ink. Therefore, with consumption of liquid 217, air will enter tube 224 forming a space in order to compensate for the volume of ink consumed. If such a space is formed and if the space expands due to increase in temperature, reduction in pressure or any other reason, liquid 217 is able to enter capillary liquid retainer 215 when tip 212 or the writing point is set upwards. Therefore, also in this case, ink will reach tip 212 via capillary liquid retainer 215 and finally the ink or liquid 217 will leak from the tip. It may be considered that this ink leakage problem occurring when the writing point or tip 212 is put upwards is solved by providing a vent near tip 212. However, when tip 212 is put downwards, since from the structure of the design, neither ink nor air will enter capillary liquid retainer 215 through valve means 220, if the air expands due to increase in temperature and/or reduction in pressure, ink will leak from the vent provided near tip 212. Thus, from a practical view point, it is difficult for the structure using the tube disclosed in Japanese Patent Application Laid-Open Hei 4 No. 227886 to provide a writing implement in which the entire ink tank can be filled up with ink.
Thus, the invention disclosed in Japanese Patent Application Laid-Open Hei 4 No. 227886, by any means, faces difficulties in filling the ink tank with ink, and has the drawback in that the entire ink tank cannot be filled up with ink.
The drawings related to the examples shown in Japanese Patent Application Laid-Open Hei 4 No. 227886, illustrate configurations in that the opening formed in air supply pipe 213 is not dipped in ink and is continuously open to the atmosphere when the writing point is set downwards. In the case as above where inner space 225 is put in communication with the atmosphere, if the pen has a low ink retention as when capillary liquid retainer 215 has a high porosity, there occurs a drawback that ink will leak forwards from the writing point. To deal with this, if a capillary liquid retainer with a low porosity is used to prevent forward leakage, the ink retention becomes high, causing difficulties in ejecting ink from the writing point, hence degrading ink supply during writing as a writing implement whilst producing drawn lines of low-density.